In terms of assets, it is an investment that will continue to depreciate, so needs to be a bridge to greater success, hence making it a gamble. The ideal situation would be to buy young, nurture, and 'own' at the players peak, which is in itself a gamble from the off.
Investing in 'ready made' will always be expensive, so if we were to go down that route, we would need to be able to afford any such depreciation should our ambitions not be met, and that is the issue with older purchases.
I guess the compromise would be to do what Moyes and his scouting team have been good at, and that is to identify players who are soon to peak, before anybody else does, and do it by way of avoiding all the costs of the nurturing.
In other words, 22-24 year old bargains.